X-ray device



July 27, 1937. H. KUNZ X-RAY DEVICE Original Filed Oct. 12, 1929 Inventor Heinrich Kunz,

His Atborngy.

Patented July 27, 1937 X-RAY DEVICE Heinrich Kunz, Erlangen, Germany, assignor to General Electric Company, a corporation of New York 2 Claims.

My invention relates to X-ray devices, and more particularly to X-ray apparatus which is energized by rectified alternating current.

This application is a division of my application Serial No. 399,334, filed October 12, 1929, entitled X-ray devices assigned to the same assignee as the present application.

The usual form of X-ray tube is provided with a filamentary cathode and a focusing cup for directing the electrons toward a cooperating anode. It has been found that when highvoltage alternating current is. applied directly to the tube, the electrons impact with the target with such a force and are constrained to such a small area as to give rise to a hot spot on the target which constitutes a virtual electron-emitting cathode on the reverse half-cycles of voltage. This reverse current tends deleteriously to affect the filamentary cathode and serves to lower the rectifying eificiency of the tube. Accordingly, in the past, it has been proposed to utilize in connection with this form of Xray tube a rectifier or valve through which the reverse current may find a ready path, thereby 25 precluding the effects referred to. The rectifier usually takes the form of a thermionic valve and is connected reversely across the terminals of the X-ray tube, that is, poled in such a manner as to offer substantially no more impedance to the flow of current than is offered by the Xray tube to current flowing in the opposite direction. The current drawn during each halfa cycle from the energizing transformer thus remains substantially the same. While an arrangement of this sort is satisfactory in operation, it calls for a complicated layout of apparatus and takes up a great deal of space besides involving considerable expense.

An object of my invention is to simplify systems of this character. This object is attained in brief by combining the valve or rectifier and the X-ray tube into a unitary compact structure. The invention will be better understood when reference is made to the drawing in which Fig. l is an elevational view, partly broken away and partly in section, of the improved apparatus; Fig. 2 shows a modified construction of the tube; Fig. 3 is a plan view of the rectifier cathode illustrated in Fig. 2; while Fig. 4 is an elevational View, partly in section, of the X-ray cathode shank.

Referring more particularly to Fig. 1, numeral l designates an evacuated envelope containing a plurality of electrodes arranged about the longitudinal axis. The electrodes include a cathode member which may take the form of a vertical spiral 2 surrounded by the usual focusing cup 3 and supported within the envelope by a shank 4, shown in section in Fig. 4. The shank mem ber consists of a metallic tube surrounding a sleeve 5 of insulation, and enclosing a conductor 6, which connects with the center or end terminal of the spiral 2. Energizing current may thus be transmitted to the latter by the shank i to which one terminal is connected, and also by the insulated conductor 6.

In opposed relation to the cathode 2 and cooperating therewith isthe usual form of tungsten copper-backed anode I supported within the envelope by means of shank 8. The electrodes 2 and l constitute the X-ray device proper, in that electrons emitted by the cathode are accelerated toward the anode at such a velocity as to produce X-rays. When high voltage is impressed directly across the anode l and cathode 2, the focusing cup 3 would normally cause the electrons to impinge on a restricted area on the target, thus producing a hot spot which, in the case of alternating voltage, causes reverse current and seriously impairs the efficiency of the tube. On the other hand, a source of alternating current is particularly desirable for energizing purposes because of the facility with which it may be transformed into current of high voltage. Accordingly, in order to improve the operation of the tube under alternating current conditions, I propose to utilize'a thermionic valve or rectifier as contemplated by the prior art, and to provide a novel arrangement of the rectifier and X-ray device.

In Fig. l the rectifying arrangement is constituted of a cathode 9, shown in the form of a longitudinal helix insulatingly supported in any suitable manner about the shank 8 and also of a cylindrical anode it, which surrounds the cathode. The cylinder I ll conveniently may be supported by stay-wires M which terminate in a collar l2 secured to the shank; these wires in addition to supporting the rectifier anode in may also serve to conduct electrical energy thereto. Conductors I3 may be led out through the envelope from the cathode 9. The electrodes for producing X-rays as well as the rectifier electrodes, are thus mounted in a co -axial manner which lends simplicity to the manufacture and assembly of the structure as a whole.

The cathodes 2 and 9 may be energized from any suitable source of electromotive force. The cathode 9 and anode it may be connected in any suitable and well-known manner to an alternating current source by which the proper voltage is impressed across the electrodes 2 and I but substantially no reverse current is caused to flow therebetween.

Fig. 2 shows an alternative arrangement in which the rectifier cathode may take the form of a flat spiral I8, shown in plan in Fig. 4, and supported from the X-ray anode shank 8 by a disk IQ of insulation material, to which rigid wires 20 are secured. These wires may be attached to equidistantly spaced points on adjacent turns of the spiral l8, as shown. The spiral may be energized through conductors (not shown) sealed in the envelope. The rectifier anode is preferably shaped as a metal plate or disk 2| spaced in parallel relation with the plane of the spiral and. secured in any suitable way to the shank 4. If desired, the focusing cup 3 and the plate 2| may be combined into a single member.

What I claim as new and desire to secure by Letters Patent of the United States, is:

1. An X-ray tube comprising an envelope containing a cathode and an anode cooperating to produce X-rays when energized by alternating current, and means within the envelope for bypassing a half-wave component of said alternating current away from. said cathode and anode, said means comprising a cathode in the form of a flat spiral and an anode formed as a disk, arranged in parallelly opposed relation with respect to said spiral and connected to the 

